Polymer blend compositions for use in engineering applications should exhibit a combination of heat resistance, good impact strength and good modulus. Additionally, the blend compositions should exhibit good melt flow properties which facilitate processing and molding of the blend compositions. Polycarbonates are popular blend components owing to their toughness and relatively high softening temperatures. However, owing to their relatively poor melt flow characteristics, polycarbonates are often blended with one or more additional polymers to improve the melt flow properties. While the resulting blends generally exhibit improved melt flow properties, other properties such as heat resistance, impact strength and the like are reduced.
Examples of such blend compositions are known. For example, the Grabowski U.S. Pat. No. 3,130,177 discloses blends of polycarbonates with polybutadiene, styrene, acrylonitrile graft polymers while the Grabowski U.S. Pat. No. 3,162,695 discloses blends of polycarbonates with butadiene-styrene, methyl methacrylate, styrene graft copolymers. The Liebig et al U.S. Pat. No. 4,205,140 discloses a thermoplastic molding composition comprising a blend of a polycarbonate, a diene rubber graft polymer such as ABS, and a styrene polymer. Similar blends of polycarbonate with styrene-maleic anhydride copolymer, ABS resin and styrene-acrylonitrile random copolymer are disclosed in the Henton U.S. Pat. No. 4,218,544. The Grigo et al U.S. Pat. No. 4,472,554 discloses thermoplastic molding compositions comprising a blend of a polycarbonate, a graft polymer such as ABS and a polymeric acidifying agent. European Patent Applications Nos. 135,492 and 135,493 also disclose polymer blends of polycarbonates, ABS polymers and styrene polymers. These blends exhibit various physical properties depending on the type and ratio of components included therein.